If people do not drink enough water, they may become dehydrated and have symptoms such as dry and sticky mouth, sunken eyes, decreased tear production, little or no urine output, and lethargy. They may also develop low blood pressure and a rapid heart rate. Humans cannot cannot survive without water. Water is necessary for breathing because it moistens the lungs. The lungs use up to a pint of water every day, and when that liquid isn’t replaced, it makes it difficult to breathe. Additionally, people who don’t get enough fluids can also gain excess body fat, have poor muscle tone and a decreased ability to digest food.